Constant envelope amplification apparatus (also referred to as outphasing amplification apparatus) have traditionally been known. In order to improve efficiency, a constant envelope amplification apparatus generates two constant amplitude signals from an input signal by vector decomposition and amplifies the two constant amplitude signals.
A linear constant envelope amplification apparatus which performs lossy combination of two amplified signals (vectors) by the use of a resistance element or a highly efficient constant envelope amplification apparatus which performs lossless combination of two amplified signals (vectors) without using a resistance element is known as a constant envelope amplification apparatus. Highly efficient constant envelope amplification apparatus are of two types according to the structure of an output combining circuit: offset type and Chireix type.
A highly efficient, highly linear power amplification apparatus using a 4-terminal power combining circuit the loss of which is reduced was provided in the past (see, for example, Japanese Laid-open Patent Publication No. 2000-349575).
With constant envelope amplification apparatus, however, higher efficiency and a flat phase characteristic in an amplification band are required.